FIG. 1 shows such a solid-state laser according to the prior art, which is distributed by the applicant under the name “VersaDisk”. The laser 100 comprises a laser amplifier 2 and a linear laser resonator 101. The laser amplifier 2 comprises a disk-shaped active medium 3 having a reflector, which is either deposited onto a back surface of the active medium 3 as a highly reflective coating, or which is formed as a separate mirror and connected with the active medium 3. The active medium 3 with the reflector rests on a cooling means 4 formed as a cooling finger, which cooling means dissipates heat from the active medium substantially perpendicular to a surface thereof.
The linear laser resonator 101 is formed by the above reflector and the concave mirror 11 serving as an output mirror for coupling out the output laser beam 19. Within the laser resonator 101 are provided an etalon 14, a Brewster plate 15 or selectively a Lyot filter 16 for enabling a selection of the wavelength, polarization and mode within the laser resonator 101. The active medium 3 is disposed at the focus of a parabolic or concave mirror 7 serving as an optical means for refocusing a pumping light. The pumping light is imaged via the glass fiber 5 and an input coupling mirror 6 disposed at a side thereof onto a mirror segment of the concave mirror 7, which images the pumping light onto the active medium 3 and focuses it. Pumping light 9b that is reflected by the reflector of the active medium 3, is reflected back onto another location or another segment of the concave mirror 7, where the pumping light is deviated onto another location or another segment of the concave mirror 7 and imaged and focused again onto the active medium 3. Thus, the pumping light is deviated repeatedly by the concave mirror 7 and is focused again onto the active medium 3 so that a multiple beam passage of the pumping light through the active medium 3 is accomplished. Thus, the effective absorption length within the active medium can be substantially larger than the thickness of the active medium 3. With regard to further details of the pumping geometry reference is made to U.S. Pat. No. 6,577,666 B2 and US 2003/25987 A1, the contents of which are hereby explicitly incorporated in the present application. A standing optical wave is formed within the laser resonator 101, which propagates through the opening 8 of the concave mirror 7.
The laser according to FIG. 1 is characterized by a high pump efficiency. Due to the homogeneous heat flow within the cooling finger 4, which serves at a heat sink, which heat flow is substantially co-linear to the optical axis of the laser resonator 101, thermal lensing effects are practically neglectible. The output laser beam 19 exhibits a nearly perfect Gaussian-shaped beam profile at all power levels so that the output laser beam 19 can be focused to small beam spots. Using a Yb:YAG crystal as the active medium 3, output powers of 10 W to 100 W at an output wavelength of 1030 nm can be achieved. The Lyot filter 16 provides for the ability of tuning the wavelength between approximately 1000 nm and approximately 1060 nm. The etalon 14 provides for a longitudinal single mode operation. The laser according to FIG. 1 can be operated in a perfect TEM00 laser operation.
However, with the laser according to FIG. 1, a stability range, where laser oscillation can be maintained reliably, is relatively narrow. In particular, the laser resonator 101 is relatively prone to tilting of both end mirrors of the linear laser resonator relative to each other. Furthermore, adjusting the laser for a stable laser operation is relatively critical with regard to the locations and angular positions of the optical elements of the laser resonator. Furthermore, disposing a frequency-multiplying crystal within a standing wave resonator according to FIG. 1 is relatively complicated, as the conditions for frequency multiplication are highly sensitive to instabilities of the linear standing wave resonator.
US 2002/0172253 A1 discloses a solid-state laser comprising a plurality of thin-disk laser amplification modules in a so-called active mirror configuration, each comprising an amplification medium, a cooling means for cooling the amplification medium and a mount for the amplification medium. A coolant flows through the cooling means. Use of an optical means for refocusing a pumping light is not disclosed. This laser is intended for very high output laser powers, but is not suitable for tuning an output wavelength. Although use of a ring resonator is disclosed, wherein a plurality of amplification modules are disposed, such a ring resonator is instable. For suppressing higher TEM laser modes, a beam extension telescope comprising two concave mirrors, is provided; an opening is disposed at a focus thereof.
DE 100 54 289 A1 discloses a solid-state laser comprising a laser amplifier disposed outside of the laser resonator. An output beam of the solid-state laser enters the external laser amplifier via an opening of a parabolic mirror, said external laser amplifier being formed by a crystal disk that is mounted on a cooling finger and is optically pumped by a pumping light beam. The pumping light beam is repeatedly imaged onto the crystal disk by the parabolic mirror in order to increase the pump efficiency of the external laser amplifier.
U.S. Pat. No. 6,577,666 B2 discloses a laser amplification system comprising a solid-state laser and a pumping light source, a pumping light beam thereof repeatedly passing through the amplification medium of the solid-state laser by means of an optical means for refocusing the pumping light. The solid-state body rests with the rear flat side on a reflector, which itself is seated on a front end of a cooling finger. A mirror disposed below an opening of the optical means for refocusing forms an end mirror of a linear laser resonator. Due to its similar configuration this laser is subject to comparable limitations, which have been discussed previously with reference to FIG. 1.
U.S. Pat. No. 5,856,996 discloses an end-pumped laser system having a linear resonator or a double z-shaped resonator.
DE 197 22 943 A1 discloses a non-planar ring laser.
U.S. Pat. No. 5,206,868 discloses a resonant non-linear laser beam converter. Furthermore, various resonator geometries are disclosed.